Traits for field identification of vaginalis and species of at different growth stages. James Eckert, University of California, Department of Science, Davis, CA; Jennifer Williams, California State University, Chico, CA; Jessica Lundberg, Lundberg Family Farms, Richvale, CA; Albert Fischer, University of California, Department of Plant Science, Davis, CA

Three species of ducksalad (Heteranthera; Pontederiaceae) are currently described as being present in California rice fields. Ducksalad species found in Sacramento Valley rice fields (Sw.) Willd. is found in California as the white-flowered form of this species although other color variants exist in other regions. Identifying characteristics include individual flowers with six tepals equally separated to the top of the corolla tube, generally rigid petioles and rarely develops elongate stems. Heteranthera rotundifolia (Kunth) Griseb. is found in White-flowered Blue-flowered Bouquet mudplantain Monochoria California as the blue-flowered form and some white variants although other colors exist in other regions. Identifying Heteranthera limosa Heteranthera rotundifolia Heteranthera multiflora Monochoria vaginalis characteristics include individual flowers with six unequally separated tepals with the middle tepal of the upper three not (Sw.) Willd. (Kunth) Griseb. (Griseb.) Horn (Burm. F.) Kunth separated all the way to the top of the corolla tube, has flexible petioles and commonly develops elongate stems that may produce roots at each node. A newly described species is Heteranthera multiflora, common name is Bouquet mud-plantain. Identifying characteristics include spikes that are longer than spathes, except on cleistogamous inflorescences; filament hairs are purple; spathes 3 or more times longer than subtending internode of flowering stem.

The 1976 Rice Field Day booklet notes ducksalad first recorded in Glenn County in 1948. It also notes a marked spread of the weed during the early 1970s. From anecdotal evidence this ducksalad was the white-flowered H. limosa. The first herbarium specimen of H. limosa was collected in Glenn County in 1966. The first blue-flowered specimen was collected in 1983 and initially identified as H. limosa by a botanist at UC Davis. A blue-flowered specimen was collected in 1991 and identified by Vern Oswald at California State University, Chico and confirmed by Charles N. Horn at Newberry College, South Carolina as H. rotundifolia. The 1983 specimen has just recently been re-examined by UC Davis herbarium curator Ellen Dean and reclassified as H. rotundifolia. One specimen of blue-flowered ducksalad located at California State University Chico that was originally identified as H. limosa has been re-examined by curator Lawrence Janeway and reclassified as H. rotundifolia. Several other specimens of blue-flowered ducksalad at other California institutions initially identified as H. limosa are also being re-examined for potential reclassification as H. rotundifolia.

Adding to the confusion between species of Heteranthera is the long term misidentification of H. rotundifolia as monochoria (Monochoria vaginalis (Burm. F.) Kunth) by most rice professionals and growers. It is unclear when this began, but is likely Immature and adult leaves due to its blue flower color. M. vaginalis is documented as being present in California rice fields, but the extent of infestation Adult plant Adult plant Adult plant is unclear. M. vaginalis is in the same family (Pontederiaceae), but has some very distinctive differences from Heteranthera. Characteristics that easily separate M. vaginalis from Heteranthera are: thin lanceolate early leaves, large waxy heart shaped adult leaves and clusters of light blue flowers that are not prominent and often open under water.

The blue-flowered ducksalad (H. rotundifolia) has largely displaced the white-flowered ducksalad (H. limosa) in most fields where it has been introduced. The displacement appears to happen within a few years after initial infestation. One possible explanation for the rapid spread is mid-season seed dispersal while flood water is moving through the field. Organic rice growers have expressed concern over the spread of the blue-flowered ducksalad due to the more aggressive creeping stem behavior. This creates a dense mat of that is more difficult to kill with the field dry down method of control. This creeping behavior also tends to pull the rice down at early stages of growth. Differential herbicide efficacy on the two Seedling Seedling Seedling Monochoria seedling Heteranthera species has not been examined.

Timeline of ducksalad infestations in the Sacramento Valley •1948 – White-flowered ducksalad reported in Glenn County1 •1954 - Earliest herbarium sample of monochoria collected at RES2 •1966 - Earliest herbarium sample of white-flowered ducksalad collected in Glenn County2 •1970’s – White-flowered ducksalad infestations spread1 •1983 - Earliest herbarium sample of blue-flowered ducksalad collected near RES, initially identified as Heteranthera limosa2 •1991 - Herbarium sample of blue-flowered ducksalad in Butte County collected near RES, identified as Heteranthera rotundifolia2 •1990’s – Blue-flowered ducksalad begins to be misidentified as monochoria3 •1990’s – 2000’s – Blue-flowered ducksalad displacing the white-flowered biotype3 •2004 - Herbarium sample of mixture of white- and blue-flowered ducksalad collected in Glenn County2 •2007 – Bouquet mudplantain (Hetreanthera multiflora) found on west side of Sacramento Valley4 •2010 – Second population of H. multiflora identified near Bayliss, Ca in Glenn County 1 1976 Rice Field Day program, California Co-operative Rice Research Foundation, Inc. Adult Leaves with deep lobes at 2 Consortium of California Herbaria available at: http://ucjeps.berkeley.edu/consortium/, August 8, 2007 Leaves with rounded tips Leaves with rounded tips Leaves with pointed tips 3 Personal communications with rice producers petiole attachment 4 Sample delivered to RES by grower

Identifying characteristics of blue flowered ducksalad and monochoria •White- and blue-flowered ducksalad (Heteranthera limosa and H. rotundifolia, respectively) have oval leaves with rounded tips and Bouquet mudplantain (H. multiflora) has kidney shaped leaves, while Monochoria vaginalis has very pointed lanceolate young leaves and pointed heart-shaped older leaves. •Monochoria leaves are generally darker green and have a more waxy surface than ducksalad. •Ducksalad has very prominent single blue flowers on long stalks, Bouquet mudplantain has several flowers on a prominent stalk, while monochoria has closely clustered blue flowers on a short stalk, often opening under water and not prominent. •Ducksalad germinates soon after flooding, flowers in about 6 weeks then senesces in about 10 weeks while monochoria germinates later and only begins to flower in about 10 weeks, after ducksalad is mostly dead. Monochoria may remain present at harvest.

Single white flower Single blue flower Multiple blue-purple flowers Cluster of blue flowers